U.S. Pat. Nos. 4,534,166; 4,542,622 and 4,606,190 describe a gas turbine engine combustor having an air pressure responsive, variable area/geometry swirler disposed about a fuel nozzle for controlling flow rate of compressor discharge air to the combustor to reduce objectionable emissions and improve combustor efficiency.
In U.S. Pat. No. 4,534,166, the swirler comprises a mechanical-type register plate throttle arrangement that controls airflow rate to the combustor and also provides different swirl angles for a take-off/cruise regime and an idle regime of engine operation. In particular, a higher swirl angle and airflow rate are provided by the register plate throttle for the idle regime than for the take-off/cruise regime of engine operation. In the "lightoff" regime, the register plate throttle prevents airflow therethrough to provide a high fuel-to-air ratio for engine ignition. Varying the quantity and the direction of discharge (i.e., swirl angle) of air from the swirler is accomplished by rotating a vane assembly relative to a stationary vaned plate using an actuable drive arm connected at one end to the rotatable vane assembly and at the other end through a spherical bearing to a unison ring whereby other swirlers associated with the combustor section of the engine can be actuated in unison.
In U.S. Pat. Nos. 4,606,190 and 4,542,622, a self-actuating nozzle guide vane (swirler) device operates to increase airflow to the combustor during higher power regimes (above idle) of engine operation in response to increases in pressure drop across the combustor during such engine operation. The nozzle guide vane device employs a continuously operating primary swirler and a secondary swirler that operates only when the pressure drop across the front (upstream end) of the combustor reaches a predetermined level. The secondary swirler comprises an annular array of secondary guide vanes carried on a spring biased slidable support member that is actuated (to slide) when the pressure differential across the slidable member reaches a predetermined value. The support member slides from a closed position to a stop-limited, full open position to admit additional air to the combustor when the predetermined value is reached.
Alternately, in these patents, the secondary swirler comprises a plurality of bimetal springs fastened on an apertured member of the combustor. The bimetal springs are openable to a full open position to admit secondary air to the secondary guide vanes upon reaching a high temperature threshold level indicative of higher engine power regimes above idle.
It is an object of the invention to provide a gas turbine engine combustor with a self-actuating, variable area/geometry swirler which can progressively vary airflow rate to the combustor inlet in response to increases in air pressure differential thereacross resulting from progressive increases in fuel flow through an associated fuel nozzle.
It is another object of the invention to provide a gas turbine engine combustor with a self-actuating, variable area/geometry swirler wherein the direction of discharge, i.e., the swirl angle, of air admitted to the combustor inlet is varied as a result of progressive variations in airflow rate.
It is still another object of the invention to provide such a combustor swirler which is free of mechanical linkages, free of relative sliding or other contact between components and thus an improvement over existing complex mechanical variable area/geometry swirlers.